There presently exists a wide variety of valves used to control the vacuum being supplied at a particular application. In particular, in the papermaking industry vacuum control valves are used extensively. In a typical situation such valves are used to regulate the suction to the suction boxes. See, for example, U.S. Pat. No. 3,766,933. An automatic valve of this nature which has been widely utilized is that sold by Albany International, assignee herein, under Model No. AES V-700. The V-700 valve, which is basically shown in FIG. 1, utilizes two back-to-back piston assemblies with different size pistons and rolling diaphragms. The movement of the pistons causes a small diaphragm to cover or uncover holes in a cylinder allowing air to flow therethrough or to stop such flow depending upon the desired vacuum. While such a vacuum controller has proven eminently satisfactory and has received wide commercial acceptance, there is a desire to improve it further.
Other valves are shown in U.S. Pat. Nos. 4,413,644; 4,390,036 and 4,466,455. U.S. Pat. No. 4,413,644 shows a bleeder valve comprising a plurality of valve members in tandem to control the vacuum in suction boxes and the like.
U.S. Pat. No. 4,390,036 provides for a vacuum controller which utilizes several plungers, one of which has several openings in its inside wall which utilizes a rolling diaphragm to close off or open access to the vacuum source and/or the atmosphere for throttling purposes, etc.
U.S. Pat. No. 4,466,455 relates to a vacuum controller which uses a reciprocal plunger and flexible diaphragm which operates as a valving mechanism. As the plunger moves one way, the diaphragm closes off the opening in the side wall of the plunger and in the opposite direction it opens the opening.
In situations where diaphragms are used to cover and uncover holes in a throttling mechanism, heavy diaphragms or Bellowframs.TM. are utilized. The heavier diaphragm results in less flexibility and response with consequential higher hysteresis. Furthermore, in certain applications, particularly in papermaking, there is a possibility contamination of the necessarily small holes used for throttling. It would therefore be desirable to provide for a vacuum controller that is flexible, responsive and avoids the use of small openings which have the chance of contaminants lodging therein.